1 //===-- llvm/MC/MCAsmBack.h - MC Asm Backend --------------------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 #ifndef LLVM_MC_MCASMBACKEND_H
11 #define LLVM_MC_MCASMBACKEND_H
13 #include "llvm/MC/MCDirectives.h"
14 #include "llvm/MC/MCFixup.h"
15 #include "llvm/Support/DataTypes.h"
16 #include "llvm/Support/ErrorHandling.h"
21 class MCELFObjectTargetWriter;
22 struct MCFixupKindInfo;
31 /// MCAsmBackend - Generic interface to target specific assembler backends.
33 MCAsmBackend(const MCAsmBackend &) LLVM_DELETED_FUNCTION;
34 void operator=(const MCAsmBackend &) LLVM_DELETED_FUNCTION;
35 protected: // Can only create subclasses.
38 unsigned HasReliableSymbolDifference : 1;
41 virtual ~MCAsmBackend();
43 /// createObjectWriter - Create a new MCObjectWriter instance for use by the
44 /// assembler backend to emit the final object file.
45 virtual MCObjectWriter *createObjectWriter(raw_ostream &OS) const = 0;
47 /// createELFObjectTargetWriter - Create a new ELFObjectTargetWriter to enable
48 /// non-standard ELFObjectWriters.
49 virtual MCELFObjectTargetWriter *createELFObjectTargetWriter() const {
50 llvm_unreachable("createELFObjectTargetWriter is not supported by asm "
54 /// hasReliableSymbolDifference - Check whether this target implements
55 /// accurate relocations for differences between symbols. If not, differences
56 /// between symbols will always be relocatable expressions and any references
57 /// to temporary symbols will be assumed to be in the same atom, unless they
58 /// reside in a different section.
60 /// This should always be true (since it results in fewer relocations with no
61 /// loss of functionality), but is currently supported as a way to maintain
62 /// exact object compatibility with Darwin 'as' (on non-x86_64). It should
63 /// eventually should be eliminated.
64 bool hasReliableSymbolDifference() const {
65 return HasReliableSymbolDifference;
68 /// doesSectionRequireSymbols - Check whether the given section requires that
69 /// all symbols (even temporaries) have symbol table entries.
70 virtual bool doesSectionRequireSymbols(const MCSection &Section) const {
74 /// isSectionAtomizable - Check whether the given section can be split into
77 /// \see MCAssembler::isSymbolLinkerVisible().
78 virtual bool isSectionAtomizable(const MCSection &Section) const {
82 /// @name Target Fixup Interfaces
85 /// getNumFixupKinds - Get the number of target specific fixup kinds.
86 virtual unsigned getNumFixupKinds() const = 0;
88 /// getFixupKindInfo - Get information on a fixup kind.
89 virtual const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const;
91 /// processFixupValue - Target hook to adjust the literal value of a fixup
92 /// if necessary. IsResolved signals whether the caller believes a relocation
93 /// is needed; the target can modify the value. The default does nothing.
94 virtual void processFixupValue(const MCAssembler &Asm,
95 const MCAsmLayout &Layout,
96 const MCFixup &Fixup, const MCFragment *DF,
97 MCValue &Target, uint64_t &Value,
102 /// applyFixup - Apply the \arg Value for given \arg Fixup into the provided
103 /// data fragment, at the offset specified by the fixup and following the
104 /// fixup kind as appropriate.
105 virtual void applyFixup(const MCFixup &Fixup, char *Data, unsigned DataSize,
106 uint64_t Value) const = 0;
110 /// @name Target Relaxation Interfaces
113 /// mayNeedRelaxation - Check whether the given instruction may need
116 /// \param Inst - The instruction to test.
117 virtual bool mayNeedRelaxation(const MCInst &Inst) const = 0;
119 /// fixupNeedsRelaxation - Target specific predicate for whether a given
120 /// fixup requires the associated instruction to be relaxed.
121 virtual bool fixupNeedsRelaxation(const MCFixup &Fixup,
123 const MCInstFragment *DF,
124 const MCAsmLayout &Layout) const = 0;
126 /// RelaxInstruction - Relax the instruction in the given fragment to the next
127 /// wider instruction.
129 /// \param Inst The instruction to relax, which may be the same as the
131 /// \param [out] Res On return, the relaxed instruction.
132 virtual void relaxInstruction(const MCInst &Inst, MCInst &Res) const = 0;
136 /// getMinimumNopSize - Returns the minimum size of a nop in bytes on this
137 /// target. The assembler will use this to emit excess padding in situations
138 /// where the padding required for simple alignment would be less than the
139 /// minimum nop size.
141 virtual unsigned getMinimumNopSize() const { return 1; }
143 /// writeNopData - Write an (optimal) nop sequence of Count bytes to the given
144 /// output. If the target cannot generate such a sequence, it should return an
147 /// \return - True on success.
148 virtual bool writeNopData(uint64_t Count, MCObjectWriter *OW) const = 0;
150 /// handleAssemblerFlag - Handle any target-specific assembler flags.
151 /// By default, do nothing.
152 virtual void handleAssemblerFlag(MCAssemblerFlag Flag) {}
155 } // End llvm namespace